Nitrogen oxides (NO, NO2, N2O) contribute to several environmental hazards including global warming, smog, ground level ozone formation, and acid rain. Emission reduction is possible through modification of combustion parameters, but reducing NOxemissions to acceptable levels requires effective aftertreatment technologies. Current catalytic NOx reduction control technologies include three-way catalysts and ammonia-based selective catalytic reduction. While these methods are highly effective for current combustion technologies, they are unsuitable for the next generation of high efficiency lean-burn natural gas engines. Three-way catalysts are inactive in oxygen rich environments, while the large size and expense of ammonia SCR installations make them an impractical solution in a distributed energy context.
NOx, trap systems have received attention as a possible solution for lean NOx removal. These traps rely on bifunctional materials to store and reduce NOx under different engine cycles. Under lean conditions NOx is ‘trapped’ on alkali metal oxides, and the engine is then periodically run under rich conditions to accomplish reduction over precious metals. These changes in engine operating conditions would necessitate additional engine controls. Additionally, current trap materials such as Ba and Pt are susceptible to sintering and SO2 poisoning.
The use of hydrocarbons as reducing agents in NO removal has attracted significant attention. The presence of hydrocarbons in current engine exhaust streams would make them a readily available and cost effective choice. However, hydrocarbon combustion, particularly in oxygen rich environments, may block NO reduction reactions.
As demands increase for methods of removing pollutants, the need arises for improved systems and methods of pollutant removal, especially systems operable to offset the hydrocarbon combustion in oxygen rich environments.